Merchants republics are among the theoretically really strong nations in the game. They have a extra merchant (giving them not only the merchant but a higher naval force limit), that have extra trade efficiency and on top of that a bonus to trade steering. Add to that the, frankly, a little bit OP ability to elect rulers. Yet you rarely see nations like Venice or the Hansa grow to conquer the world. One reason for this is their geographical weakness, especially the Hansa lacks strategic depth. Then add that to what I mentioned earlier, the trade republics are kind of dangerous. This, first order of business for Denmark - take out the Hansa and for Austria - take out Venice. So we started thinking, what kind of extra thing can we add to an expansion that adds an extra layer to the Merchant Republics.
This is interesting coming from EU4 devs considering that the forum consensus is that republics suck really, really badly in comparison to monarchies. Sure, Republics can choose leaders, but Monarchies have better government bonuses, legitimacy gives better bonuses than republican tradition, it is far easier to gain legitimacy than it is republican tradition, republics have to pay more for stab and republics get horrible events that really cripple them. To top it off, the starting merchant republics have terrible, terrible NIs. Put all those together and theres very good reason why theres no incentive or reason to go republic at all. Also, as others have said, theres really nothing to spend money on other than going obscenely over your force limits, which really limits the 'strategy' portion of the game. Infact, im not even sure what the point of this expansion is going to be considering that money really does not have much use in the metagame at the moment due to your primary limitations being monarch points, and its even more insane that the large numbers of new mechanics that are being added to the game are all dependant on monarch points which are already the scarcest resource while money still has no decent sinks aside from moar troops.